We will develop and evaluate a novel gamma imaging probe for lymphatic node mapping and sentinel lymph node dissection. This imaging probe would significantly increase the sensitivity, resolution and specificity over the currently available operative devices. It will also potentially reduce the time duration and the costs for the procedures. In Phase I of the project, we will design and build the imaging probe test it in phantom experiments, and explore ways to optimize its performance. The novel detector design that we will investigate consists of 169 pieces of scintillating crystals optically connected to a position sensitive PMT (1"x 1"). The proposed novel imaging probe is small enough to be inserted into surgical incisions for node detection. This allows close proximity to the source of radiation to enhance the resolution and sensitivity for detecting sentinel lymph nodes. We have previously developed a larger intraoperative camera (3.5 inches diameter). The proposed imaging probe uses the same electronics and software used in our intraoperative camera. This greatly expedites the development of the proposed imaging probe. During Phase II the imaging probe and the intraoperative gamma camera will be evaluated in melanoma and breast cancer operations. PROPOSED COMMERCIAL APPLICATION: Radio-guided lymphatic mapping and disection is standard care in melanoma, and standard procedure in management of breast cancer. Our company's sole mission is to bring the power of nuclear imaging into the operating room. This proposed imaging probe will generate a substantial revenue for our company in the near future.